1. Field of the Invention
The present invention relates generally to a radiation detector and a radiation measurement system, which utilize a scintillator. More specifically, the invention relates to a radiation detector and a radiation measurement system, which can be applied in a high-temperature environment or in a temperature changing environment.
2. Description of the Related Art
Conventionally, there is known a radiation detector utilizing a scintillator for emitting a scintillation light in response to an incoming radiation. Examples of such conventional radiation detectors are shown in FIGS. 9 and 10.
First, the radiation detector shown in FIG. 9 comprises a scintillator 1 for emitting a scintillation light in response to an incoming radiation, a light guide (a main light guide) 4 optically connected to the scintillator 1 via an optical coupling material 3, and a wavelength shift fiber 5 passing through the light guide 4 (see "Optical Waveguide Scintillator" disclosed in Japanese Patent Laid-Open No. 6-258446).
The light guide 4 is surrounded by reflecting surfaces for inwardly reflecting the incoming scintillation light, except for a plane of incidence (a plane connected by the optical coupling material 3), on which the scintillation light emitted from the scintillator 1 is incident. The scintillation light entering the light guide 4 is stochastically incident on the wavelength shift fiber 5 by the function of the reflecting surfaces in a process where the light guide 4 is filled with the scintillation light.
The wavelength shift fiber 5 is designed to absorb the incoming scintillation light to re-emit light of a longer wavelength (fluorescent pulses) simultaneously from both end portions thereof.
The light emitted from both end portions of the wavelength shift fiber 5 are guided by light guiding fibers 6A and 6B to signal processing parts 7A and 7B, each of which comprises a photodetector and so forth, to be converted into electric pulses therein.
In such a radiation detector, electronic circuit parts, such as the signal processing parts 7A and 7B, can be arranged apart from the scintillator 1.
The radiation detector shown in FIG. 10 comprises a scintillator 1, and a signal processing part 17, which comprises a photodetector and so forth and which is directly connected to the scintillator 1 via an optical coupling material 3. In this radiation detector, since a scintillation light emitted from the scintillator 1 is directly incident on the signal processing part 17, the loss of the scintillation light is small, so that it is possible to obtain high radiation counting sensitivity.
In the case of the radiation detector shown in FIG. 10, the detector itself includes electronic circuit parts in the signal processing part 17. On the other hand, the radiation detector shown in FIG. 9 has the advantage of heat resistance since it is not required to provide any electronic circuits in the vicinity of the detector itself (the upper limit to the heat resisting temperatures of typical electronic circuits is about 50.degree. C.).
In the radiation detectors described above, there is the following problem. That is, although there are some of scintillators 1 having a heat resisting temperature of about 200.degree. C., the wavelength shift fiber 5 of component parts has only a heat resisting temperature of 70.about.80.degree. C. since it is made of a plastic material, such as a polystyrene or a methacrylic resin. At present, there are no alternative parts having a higher heat resisting temperature, so that there is a problem in that conventional radiation detectors can not be used in an environment of a temperature exceeding 70.about.80.degree. C.
In addition, when the radiation detector is provided in a temperature changing environment, it is difficult to hold the radiation measurement accuracy in accordance with such a temperature change. Particularly in the radiation detector shown in FIG. 10, the scintillator 1 is substantially integrated with the signal processing part 17, and the difference in heat conduction in component parts and the difference in the influence of temperature are intricately intertwisted. Therefore, it is not easy to carry out a temperature correction in the measurement of radiation since it is required to provide temperature compensating circuit means for controlling a high voltage applied to the photodetector by means of a thermistor, or an optical pulser for drift monitoring.